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Intermolecular Forces andLiquids and Solids
Chapter 11
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Phase: homogeneous part of the system in contact with otherparts of the system but separated from them by a well-definedboundary.
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Forces
Intermolecular forcesare attractive forces between molecules.
Intramolecular forceshold atoms together in a molecule.
Intermolecular vs Intramolecular
41 kJ to vaporize 1 mole of water (inter)
930 kJ to break all O-H bonds in 1 mole of water ( intra)
Generally, intermolecular
forces are much weakerthan intramolecular forces.
Measure of intermolecular force
boiling point
melting point
DHvap
DHfus
DHsub 4
Intermolecular Forces
Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
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Intermolecular Forces
Ion-Dipole Forces
Attractive forces between an ion and a polar molecule
Ion-Dipole Interaction
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in solution
EX: Interaction Between Water and Cations
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Intermolecular Forces
Dispersion Forces
Attractive forces that arise as a result of temporarydipoles induced in atoms or molecules
ion-induced dipole interaction
dipole-induced dipole interaction
Neutral
molecule
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Induced Dipoles Interacting With Each Other
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Intermolecular Forces
Dispersion Forces Continued:
Polarizability: the ease with which the electron distribution inthe atom or molecule can be distorted
Polarizability increases with:
greater number of electrons
more diffuse electron cloud
Dispersion forces usually
increase with molar mass
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S
EX:What type(s) of intermolecular forces existbetween each of the following molecules?
HBrHBr is a polar molecule: dipole-dipole forces. There arealso dispersion forces between HBr molecules.
CH4CH4 is nonpolar: dispersion forces.
SO2SO2 is a polar molecule: dipole-dipole forces. There arealso dispersion forces between SO2 molecules.
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Intermolecular Forces
Hydrogen Bond : a special dipole-dipole interaction betweenthe hydrogen atom in a polar N-H, O-H, or F-H bond and anelectronegative O, N, or F atom.
A HB A HAor
A & B are N, O, or F
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Hydrogen Bond
HCOOH and water
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Why is the hydrogen bond considered a special
dipole-dipole interaction?
Decreasing molar massDecreasing boiling point
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Properties of Liquids
Surface tension: the amount of energy required to stretchor increase the surface of a liquid by a unit area.
Strongintermolecular
forces
Highsurfacetension
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Properties of Liquids
Cohesion:the intermolecular attraction between likemolecules
Adhesion:an attraction between unlikemolecules
Adhesion
Cohesion
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Properties of Liquids
Viscosity: a measure of a fluids resistance to flow
Strongintermolecular
forces
Highviscosity
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Density of Water
Maximum Density40C
Ice is less dense than water
Water is a Unique Substance3-D Structure of Water
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crystalline solidpossesses rigid and long-range order. In acrystalline solid, atoms, molecules or ions occupy specific(predictable) positions.
amorphous soliddoes not possess a well-defined
arrangement and long-range molecular order.
unit cellis the basic repeating structural unit of a crystallinesolid.
latticepoint
Unit Cell Unit cells in 3 dimensions
At lattice points:
Atoms
Molecules
Ions
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An Arrangement for Obtaining the X-ray Diffraction Patternof a Crystal.
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Types of Crystals
Ionic Crystals Lattice points occupied by cations and anions
Held together by electrostatic attraction
Hard, brittle, high melting point
Poor conductor of heat and electricity
CsCl ZnS CaF2
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Types of Crystals
Covalent Crystals Lattice points occupied by atoms
Held together by covalent bonds
Hard, high melting point
Poor conductor of heat and electricity
diamond graphite
carbonatoms
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Types of Crystals
Molecular Crystals Lattice points occupied by molecules
Held together by intermolecular forces
Soft, low melting point
Poor conductor of heat and electricity
water benzene
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Types of Crystals
Metallic Crystals Lattice points occupied by metal atoms
Held together by metallic bonds
Soft to hard, low to high melting point Good conductors of heat and electricity
Cross Section of a Metallic Crystal
nucleus &inner shell e-
mobile sea
of e-
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Crystal Structures of Metals
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Types of Crystals
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A glassis an optically transparent fusion product of inorganicmaterials that has cooled to a rigid state without crystallizing
Crystallinequartz (SiO2)
Non-crystallinequartz glass
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Chemistry In Action: High-Temperature Superconductors
MgB2
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Chemistry In Action: And All for the Want of a Button
white tin grey tinT < 13 0C
stable weak
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LeastOrder
Phase Changes
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T2 > T1
Effect of Temperature on Kinetic Energy
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Equilibrium vapor pressureis the vapor pressuremeasured when a dynamic equilibrium exists between
condensation and evaporation
H2O (l) H2O (g)
Rate ofcondensation
Rate ofevaporation
=
Dynamic Equilibrium
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BeforeEvaporation
AtEquilibrium
Measurement of Vapor Pressure
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Molar heat of vaporization(DHvap) is the energy required tovaporize 1 mole of a liquid at its boiling point.
ln P= -DHvap
RT+ C
Clausius-Clapeyron Equation
P= (equilibrium) vapor pressure
T= temperature (K)
R= gas constant (8.314 J/Kmol)
Vapor Pressure Versus Temperature
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Alternate Forms of the Clausius-Clapeyron Equation
At two temperatures
or
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boiling pointis the temperature at which the (equilibrium)vapor pressure of a liquid is equal to the external pressure.
The normal boiling pointis the temperature at which a liquidboils when the external pressure is 1 atm.
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The critical temperature(Tc) is the temperature above whichthe gas cannot be made to liquefy, no matter how great theapplied pressure.
The critical pressure(Pc) is the minimumpressure that must beapplied to bring about
liquefaction at thecritical temperature
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The Critical Phenomenon of SF6
T < Tc T > Tc T ~ Tc T < Tc
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H2O (s) H2O (l)
The melting pointof a solidor the freezing pointof aliquid is the temperature atwhich the solid and liquidphases coexist in equilibrium
Solid-Liquid Equilibrium
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Molar heat of fusion(DHfus) is the energy required to melt1 mole of a solid substance at its freezing point.
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Heating Curve
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H2O (s) H2O (g)
Molar heat of sublimation(DHsub) is the energy requiredto sublime 1 mole of a solid.
DHsub = DHfus + DHvap( Hesss Law)
Solid-Gas Equilibrium
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A phase diagramsummarizes the conditions at which asubstance exists as a solid, liquid, or gas.
Phase Diagram of Water
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Phase Diagram of Carbon Dioxide
At 1 atmCO2 (s) CO2 (g)
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Effect of Increase in Pressure on the Melting Pointof Ice and the Boiling Point of Water
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Chemistry In Action: Ice Skating